The present invention relates to an automatic computing tonometer system and method; and more particularly, it relates to a computerized ocular tonometer and a method of recording tonometry measurement data and computing the required test results which include the intraocular pressure, the "C" value and the flow value for an eye under test. The invention also relates to a unique tonometer handpiece which gives a clinician visual information relating to the test and results.
Electronic tonometers and tonographers are known in the art. Examples of currently available systems include the model OP9100 Inkles Tonographer and the Model OP9102 Electronic Tonometer, both manufactured by V. Mueller and Company, Chicago, Ill. Each of these instruments includes a tonometer handpiece which, as will be described in greater detail within, has a member, referred to as a "plunger" which rests on the eye under test. The weight of the plunger is known. The plunger will indent the surface of the eyeball under gravity, and the indentation is resisted by the intraocular pressure.
The handpiece includes a transducer which is an electro-mechanical device which generates an electrical signal, the phase of which is representative of the position of the plunger relative to its initial position.
As will be explained in more detail within, this signal is fed to a phase detector which generates an output signal having an amplitude representative of plunger displacement. This signal may be displayed on a meter having a scale measured in tonometric units, or it may be recorded, as on graph paper. In either case, it is not the actual measurement or graph which provides the useful or desired test results; rather, the test results such as intraocular pressure, P0, the C value CV, and flow value FV, are calculated from the displacement measurements, together with other information such as Corneal Curvature (CC), Ocular Rigidity (OR), and Aplanation Reading (AR). These other parameters are sometimes referred to herein as "Other Test Parameters". The actual calculation of the results may involve considerable table look-up, in addition to actual computation.
The test results may be greatly affected by various known artifacts, and if extreme accuracy is required, certain correction factors should be taken into consideration. One such artifact is a transient pressure within the eye caused by a temporary increase in blood pressure which may accompany placing the instrument on a subject's eye.
Because of the difficulty in eliminating the effects caused by these artifacts and the time required to determine the correction factors in using pencil and paper or a hand calculator, they usually are not made. The resulting computations of intraocular pressure, C value, and flow value are, therefore, not as accurate as they might be.
In its broader aspects, the present invention uses a high-speed digital computer with a conventional tonometer head (transducer) and measuring circuitry for computing very accurate results for interocular pressure, C value and flow value, eliminating artifacts and applying correction factors with or without operator intervention. For example, based upon Aplanation readings made before the test is conducted, the aplanation measurements may be fed into the system, and values of ocular rigidity, corneal curvature, and intraocular pressure may be computed accurately and rapidly. The more accurate results show up, of course, in the computed results for C value and flow value since these depend on the corrected test parameters and intraocular pressure. Thus, one of the principal advantages of the present invention is that the computer results are more accurate than have heretofore, in general, been produced in the past due to the extremely complex and difficult hand calculations required for correction factors. Further, a decision as to whether or not to include these correction factors is taken out of the hands of the clinician and automatically incorporated into the computation of end results. Still further, artifacts such as the initial pressure increase due to anxiety are eliminated automatically, as will be discussed. The speed of computation is so great that, for all practical purposes, the results are available immediately after test.
The digital computer used as an element in the inventive system is a programmed digital computer because such computers are readily available on the market at reasonable value and because of the great flexibility in the use of such computers. However, the programming is incorporated into the machine when sold, and even though it may be modified or replaced completely on a machine in the field, no programming is required of the clinician, although he may enter data by means of a keyboard. A fixed-wired computer may equally well by employed with the present invention, as persons skilled in the art will appreciate. However, some flexibility may be lost, and as mentioned, programmable computers with sufficient capacity are available at reasonable cost.
Each test is carried out under control of the computer which is driven by a real time clock. The clock is actuated in response to placing the tonometer in test position on an eye. The computer takes the tonometer measurements at predetermined times, as determined by the Real Time Clock, and stores the data in a Random Access Memory, together with signals representative of the other test parameters. From this data, the computer calculates interocular pressure, the C value and the flow value, incorporating correction factors as needed and eliminating artifacts. These computed results are also stored in the memory. An important aspect of the present system is that it is totally flexible and easily capable of adapting to new computations or corrections as the field progresses.
A keyboard which is used to enter the other test parameters into the system may also be used to enter tonometer test measurements, for example, from a previous test. In this case, the computer may likewise be used to compute interocular pressure, C value, and flow value. This feature may be invaluable to a research technician going back into medical archives in performing basic research.
Because the present invention contains a Real Time Clock which keeps track of the tonometer readings and records the time of each reading for calculating the end results, it is possible to abbreviate most tonograms from the conventional four-minute period to a shorter period, such as two minutes. This, of course, would reduce the overall time required for testing, and particularly that portion of the test in which a plunger rests on the patient's eye.
As mentioned, the measurements and results of a given test, together with the other test parameters, are stored in memory. This gives the clinician the ability to speculate on the results of a given test by altering the measurement values for other test parameters (to account for various correction factors) on a trial basis, then computing the end results again. By studying whether or not the various combinations of correction factors effect the end result, the clinician can assure himself that the interocular pressure, coefficient of outflow, and flow value or correct under varying conditions.
The invention also includes a novel handpiece which has a pair of signal lights, preferably one is red and one is green. These lights are energized by control logic circuitry for indicating to the clinician taking the test the exact status of the test, whether the results being obtained are satisfactory, and whether current or old test data is stored in the memory. This is done without requiring that the clinician divert his attention from the handpiece which, it will be appreciated, is in contact with an eye during test. Thus, in addition to the greater accuracy afforded by a high-speed digital computer, the substantially reduced computation time, the elimination of artifacts and the automatic incorporation of correction factors, the present invention has significant operational advantages over the prior art.
Other features and advantages of the present invention will be apparent to persons skilled in the art from the following detailed description of a preferred embodiment accompanied by the attached drawing wherein identical reference numerals will refer to like elements in the various views.